Apparatuses for applying a hot-melt adhesive, a so-called hot melt, to a substrate, in particular to a so-called disposable hygiene product, such as diapers or sanitary napkins, are already basically common knowledge from the prior art.
Particularly advantageous apparatuses have been developed, for example, as disclosed in commonly owned EP 1 429 029 A2, which discloses a corresponding apparatus in which use is made of so-called volumetric gear pumps in order to provide for precise metering of the quantity of molten adhesive which is to be dispensed. The adhesive actually exits from the dispensing nozzle (for example a slot nozzle) here on account of the prevailing pressure of the adhesive, for example once a delivery valve has been opened. In some cases, the exiting adhesive is also supplied heated modulation air, which is intended to delimit the exiting adhesive with shaping action, if appropriate it is subjected to turbulence or the like, en route to the substrate located beneath. The exit from the nozzle here always takes place on account of the prevailing adhesive pressure.
Even though such apparatuses operate optimally basically in most application cases, there are application cases in which in particular more complex application patterns of the hot-melt adhesive are desired.
Further known application systems apply a pattern using rotating cylindrical screens (rotary screen systems), in which the adhesive is dispensed onto the substrate from a stationary dispensing nozzle in the interior of the rotating cylinder, through the surface bearing a punched pattern. It is typically the case here that the substrate is brought into contact with the outer cylinder surface. The adhesive pressure here can prevail in particular permanently on the nozzle and, depending on the position of the cylinder surface, is alternately prevented from exiting and allowed to pass through, and therefore a pattern is produced on the contacting substrate. Pianalto, U.S. Pat. No. 4,911,948 discloses an example of an apparatus in which a regulated air pressure prevails on the adhesive store. In practice, however, such apparatuses have problems where the application pattern is concerned, in particular smearing.
Finally, there are also application systems in which application rollers which have, on their surface, either hollows or protuberances for retaining the adhesive are brought into contact with a substrate during their rotation. A corresponding apparatus is disclosed in EP 0 675 183 A1, wherein the rubber-coated heating roller has rubber protuberances on which a hot-melt-adhesive powder, that is to say not an adhesive which is already in a molten state, is deposited and dispensed under pressure, via the protuberances, onto the substrate. It is considered to be problematic in the case of such apparatuses, that such apparatuses are very complex and costly to produce. In addition, such systems usually do not achieve application speeds desired in particular for use with hygiene articles.
It is therefore an object of the present invention to provide an apparatus which is intended for applying hot-melt adhesives and allows for precise and reliable application along with optimal utilization of the adhesive used.